Oxygenated volatile organic compounds (OVOCs) first detected from IASI : understanding the sources

Transcription

1 Oxygenated volatile organic compounds (OVOCs) first detected from IASI : understanding the sources T. Stavrakou, J.-F. Müller Belgian Institute for Space Aeronomy, Brussels L. Clarisse, P. F.Coheur, D. Hurtmans, C. Clerbaux J. Peeters Thanks to C. Vigouroux, M. De Mazière, N. Deutscher, D. Griffith, N. Jones, C. Paton-Walsh

2 CH 3 OH HCOOH Abundant over forests in the growing season, impact on OH concentrations in the PBL Major contributor to acidic rain in remote environments, but models underpredict severely the observed HCOOH concentrations missing sources Oceans 22% Primary biogenic 54% MEGANv2.1 emission model Secondary 16 % 5% 3% A priori global budget Secondary : dominant but most uncertain source! Global source = 193 Tg/yr, Τ = 6 days Global source = 36 Tg/yr, Τ = 4 days

3 CH cm cm -1 Very weak absorption interfered by other molecules, especially ozone Retrieval based on ΔT b between the target channel and nearby reference channels in the spectrum baseline Razavi et al., ACP, 2011

4 2009 IASI CH 3 OH column IMAGESv2 CH 3 OH column molec cm -2 High columns over the majority of continental regions Large overestimations over Amazonia (factor of 2-3), Africa &Indonesia (1.5-2), moderate over Europe, Eastern US

5 IASI HCOOH column - July IMAGESv2 HCOOH column molec cm -2 Strongly enhanced columns over central Africa, S. America, and boreal regions Important underestimations (factor of 2-3)

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7 IASI CH 3 OH column IMAGESv2 CH 3 OH column 193 Tg/yr Optimized CH 3 OH column Global a posteriori biogenic CH 3 OH source very close to the a priori MEGANv2.1 BUT Stavrakou et al. ACP, molec cm Tg/yr

8 Strong flux increases in arid/semi-arid regions in central Asia (x5), western US (x2) underestimated methanol rate from shrub or an unaccounted methanol source in MEGANv2.1? Biogenic emission update Significant reductions over the tropical forests in the Amazon (40-55%) and Indonesia (45-60%) FTIR IASI prior optimized prior optimized 8 South America

9 Biogenic emission update FTIR supports IASI-derived decrease in biogenic emissions over Central & S. Africa IASI FTIR prior optimized Observed seasonality well reproduced by the model Stavrakou et al. ACP, 2011 Vigouroux et al. ACP, 2012

10 INTEX-A (Jul 1-Aug 14 N. America) Very good agreement with aircraft data in PBL Biogenic emission update NEAQS : 2.8 ppb in BL Prior : 3.1 ppb Underestimation in the free troposphere : related to model underestimation in the Western US? Optimized : 2.9 ppb

11 Prior Optimized Stavrakou et al. ACP, 2011 Wells et al. ACP, 2012 In mid-latitudes IASI is maximum in spring and early summer, i.e. 1-2 months earlier than the model peak, similarly for CH 3 OH from TES (Wells et al., 2012) and tower measurements in the US Midwest (Hu et al., 2012) Emissions from new leaves are underestimated in MEGAN, and emissions from mature leaves should be decreased important changes in leaf age classes for broadleaf trees

12 Optimize the global HCOOH source: assume that missing HCOOH is produced through OH-oxidation of as-yet-unidentified biogenic precursors IASI HCOOH column IMAGESv2 HCOOH column July IASI molec cm -2 Strong biogenic HCOOH source : ~ 3 x larger than in the a priori, ~90% of the global source Enhanced emission over boreal forests likely reflecting oxidation of BVOC from conifers 36 Tg/yr Optimized HCOOH column 102 Tg/yr

13 The distribution of the extra biogenic source suggests that oxidation of terpenoids leads to substantial amounts of HCOOH Should the entire missing source of HCOOH be due to monoterpenes only, a molar yield of 200% HCOOH would be required Stavrakou et al. Nature Geosci., 2012

14 Seasonal variation of the normalized monthly emission Summertime maximum Relatively high emissions also in spring at high latitudes, in agreement with field studies on monoterpene emissions Field measurements over boreal forests point towards the existence of large emission of undetected shortlived organic compounds (Di Carlo et al. Science, 2004)

15 Comparison with FTIR data Wollongong A priori mean underestimation by factor of 3-4 excellent agreement after inversion Comparison with airborne data (INTEX-B) Region Observed A priori Optimized Western US 490 ppt North Pacific 140 ppt Comparison with ground-based data HCOOH Observed A priori Optimized Gas-phase (ppbv) Rain (μmol/l) Reunion Isl.

16 Impact of the additional biogenic HCOOH on precipitation acidity ph reduced by over boreal forests in summer, in the Tropics Calculated contribution of HCOOH to the total concentration of [H+] HCOOH accounts for as much as 6080% of the rainwater acidity over Amazonia and boreal forests in summertime

17 Conclusions Revisited the CH 3 OH & HCOOH global distribution and budget CH 3 OH : globally inferred biogenic source : ca. 100 Tg/yr, IASI suggests higher emissions over arid regions, and lower over tropical forests, supported by independent data, issues with seasonality in the mid-latitudes HCOOH : biogenic secondary source ~ 90% of the total source, originates mostly in boreal and tropical forests high-yield product in the oxidation of organic compounds, such as monoterpenes and other terpenoids IASI measurements pave the way to a better understanding of the origin and fate of oxygenated compounds